Assembly of a Micro-Hotspot of Caenogastropod Endemism in the Southern Nevada Desert, with a Description of a New Species of Tryonia (Truncatelloidea, Cochliopidae)
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A peer-reviewed open-access journal ZooKeys Assembly492: 107–122 of (2015)a micro-hotspot of caenogastropod endemism in the southern Nevada desert... 107 doi: 10.3897/zookeys.492.9246 RESEARCH ARTICLE http://zookeys.pensoft.net Launched to accelerate biodiversity research Assembly of a micro-hotspot of caenogastropod endemism in the southern Nevada desert, with a description of a new species of Tryonia (Truncatelloidea, Cochliopidae) Robert Hershler1, Hsiu-Ping Liu2, Jeffrey S. Simpson2 1 Department of Invertebrate Zoology, Smithsonian Institution, P.O. Box 37012, Washington, DC 20013- 7012, USA 2 Department of Biology, Metropolitan State University of Denver, Denver, CO 80217, USA Corresponding author: Robert Hershler ([email protected]) Academic editor: T. Backeljau | Received 13 January 2015 | Accepted 16 March 2015 | Published 30 March 2015 http://zoobank.org/8C3C5DD3-7424-49EC-9444-E07917D82DBE Citation: Hershler R, Liu H-P, Simpson JS (2015) Assembly of a micro-hotspot of caenogastropod endemism in the southern Nevada desert, with a description of a new species of Tryonia (Truncatelloidea, Cochliopidae). ZooKeys 492: 107–122. doi: 10.3897/zookeys.492.9246 Abstract Newly obtained and previously published sequences of the cytochrome c oxidase subunit I (COI) gene were analyzed to examine the biogeographic assembly of the caenogastropod fauna (belonging to the fami- lies Assimineidae, Cochliopidae, and Hydrobiidae) of an isolated spring along the lower Colorado River in southern Nevada (Blue Point Spring). Based on available COI clock calibrations, the three lineages that comprise this fauna are 2.78–1.42 million years old, which is roughly coeval or slightly younger than the age of Blue Point Spring (inferred from local fossil spring deposits). Two of the lineages—endemic Pyrgu- lopsis coloradensis and Assiminea aff. infima—are most closely related to snails in the Death Valley area (well to the west) and likely colonized Blue Point Spring by transport on birds. A single haplotype was detected in both of these snails, suggesting that they may have only recently colonized Blue Point Spring. The third lineage—endemic Tryonia infernalis, newly described herein based on morphological and molecular evidence—is most closely related to a geographically proximal species in a lower Colorado River tributary (T. clathrata); the split between these taxa may be the product of vicariance (severance of a prior drainage connection) or a separate jump dispersal event. The considerable genetic diversity inT. infernalis (three haplotypes differing by 0.6% mean sequence divergence) suggests a possibly lengthy history of local differ- entiation. Our findings also identify Blue Point Spring as a new micro-hotspot of groundwater-dependent biodiversity in Nevada and will assist ongoing efforts to protect and conserve these imperiled ecosystems. Copyright Robert Hershler et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 108 Robert Hershler et al. / ZooKeys 492: 107–122 (2015) Keywords Gastropoda, Assimineidae, Hydrobiidae, western United States, aquatic snails, biogeography, taxonomy, conservation Introduction The desert region of southeastern California and southwestern Nevada, encompassing portions of the Great Basin and lower Colorado River watershed, contains distinctive assemblages of tiny caenogastropods—belonging to the families Assimineidae (genus Assiminea), Cochliopidae (Tryonia) and Hydrobiidae (Pyrgulopsis)—that have been a recent focus of biogeographic study using mtDNA sequence data (e.g., Hershler et al. 1999a, b, Hershler and Liu 2008a, b). These assemblages broadly overlap geographi- cally and are tightly linked with spring habitats; their biogeographic histories do not well correlate with surface drainage and have likely been shaped, at least in part, by overland dispersal on waterfowl (e.g., Liu et al. 2003, Hershler et al. 2005, Liu and Hershler 2007, Hershler and Liu 2008a). The biogeographic patterns of these assem- blages also differ in important respects. The regional assimineids (referred to herein as the Assiminea infima complex) are amphibious animals that typically live on riparian vegetation along the margins of springs and spring runs. This assemblage belongs to a single lineage that diverged from marine (Pacific) coastal progenitors during the late Pliocene (Hershler and Liu 2008a). The other two assemblages are entirely aquatic: Tryonia is restricted to thermal waters while Pyrgulopsis lives in ambient temperature and thermal habitats. Both of these assemblages are composed of multiple lineages, some having long histories of diversification within the region (Hershler et al. 1999a, Hershler et al. 2011). The Tryonia assemblage is composed of a few subgroups that have close relationships with congeners from the lower Colorado River basin (T. an- gulata Hershler), northern Great Basin and western California (T. margae Hershler, T. salina Hershler), and northeastern Mexico (T. porrecta [Mighels, 1845]; clade com- posed of T. elata Hershler, T. ericae Hershler, T. variegata Hershler) (Hershler et al. 1999a, Hershler et al. 2011). ThePyrgulopsis assemblage contains a much larger num- ber of lineages which have close relationships to taxa from western California, the lower Colorado River basin, and other portions of western North America (Hershler and Liu 2008b, Hershler et al. 2013). The A. infima complex is subdivided into a clade that is distributed in the Death Valley region (this lineage also contains a population from the head of the Gulf of California) and a genetically divergent population (A. aff. infima Berry) in Blue Point Spring (Hershler and Liu 2008a), which is located along Lake Mead ca. 150 km to the east-southeast (Fig. 1). Blue Point Spring also contains an endemic species of Pyrgulop- sis (P. coloradensis Hershler) and a population of Tryonia that was previously assigned to widely ranging T. porrecta (Hershler 2001), neither of which have been previously studied genetically. Here we analyze newly obtained and previously published DNA sequences to examine the intersection of the biogeographic histories of the three con- Assembly of a micro-hotspot of caenogastropod endemism in the southern Nevada desert... 109 Figure 1. Map showing the location of Blue Point Spring relative to other geographic areas discussed in the text. The collecting localities for specimens of Pyrgulopsis sanchezi and Tryonia clathrata (sister taxa of Blue Point Spring endemics) used in the molecular phylogenetic analyses are also shown. trasting groups of snails at this isolated spring. We also describe the Blue Point Tryonia as a new, endemic species based on molecular and morphologic evidence. Our results reveal a complex historic assembly of the Blue Point Spring snail fauna; and delineate this water body as another micro-hotspot of groundwater-dependent biodiversity in the region, which will assist ongoing efforts to protect and conserve these imperiled ecosystems (Greenwald and Bradley 2008, Abele 2011). Methods Fresh material was collected from Blue Point Spring by RH in May, 2014, and preserved in 90% ethanol for genetic analysis; a portion of the T. porrecta sample was relaxed with menthol crystals, fixed in dilute (4%) formalin, and preserved in 70% ethanol for anatomical study. Genomic DNA was extracted from entire snails (A. aff. infima, six 110 Robert Hershler et al. / ZooKeys 492: 107–122 (2015) specimens; P. coloradensis, four specimens; T. porrecta, six specimens) using a CTAB pro- tocol (Bucklin 1992); each specimen was analyzed for mtDNA separately. LCO1490 and HCO2198 (Folmer et al. 1994) were used to amplify a 710 base pair (bp) frag- ment of the cytochrome c oxidase subunit I gene (COI). Amplification conditions and sequencing of amplified polymerase chain reaction product were those of Liu et al. (2003). Sequences were determined for both strands and then edited and aligned using SEQUENCHERTM version 5.0.1. Novel haplotypes were not detected in the newly sequenced specimens of A. aff. infima and thus we did not update our previously pub- lished phylogenetic analysis of the A. infima complex (Hershler and Liu 2008a). The newly sequenced specimens of Blue Point Spring Tryonia were analyzed together with previously published sequences from 30 congeners and closely related Minckleyella bal- nearis Hershler, Liu & Landye (a monotypic genus from northern Mexico), with Mex- ipyrgus carranzae Taylor used to root the phylogenetic tree (per Liu et al. 2001). Given that Pyrgulopsis is a large genus containing 139 species (Hershler et al. 2014), most of which have been previously sequenced, we restricted our analysis of the relationships of P. coloradensis to the newly sequenced specimens from Blue Point Spring, and sequences of 18 congeners from adjacent areas (including those that were found to be most similar to the newly obtained haplotypes using a BLAST search) to obtain a readable tree. The phylogenetic tree for this dataset was rooted with Floridobia winkleyi (Pilsbry) (per Her- shler et al. 2003). One example of each haplotype detected in a given sample was used in the phylogenetic analyses. The new sequences from Blue Point Spring populations were deposited in GenBank (accession numbers KP899916–KP899919). MRMODELTEST 2.3 (Nylander 2004) was used to obtain an appropriate sub- stitution model (using the Akaike